This invention relates to thermal ink jet printing systems and, more particularly, to a printer incorporting an ink delivery system which enables operation, selectively, process color, monochrome or highlight color modes.
Thermal ink jet printers are well known in the prior art as exemplified by U.S. Pat. Nos. 4,463,359 and 4,601,777. In the systems disclosed in these patents, a thermal printhead comprises one or more ink-filled channels communicating with a relatively small ink supply chamber at one end and having an opening at the opposite end, referred to as a nozzle. A plurality of thermal energy generators, usually resistors, are located in the channels at a predetermined distance from the nozzle. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. As the bubble grows, the ink bulges from the nozzle and is contained by the surface tension of the ink as a meniscus. As the bubble begins to collapse, the ink still in the channel between the nozzle and bubble starts to move towards the collapsing bubble, causing a volumetric contraction of the ink at the nozzle and resulting in the separating of the bulging ink as a droplet. The acceleration of the ink out of the nozzle while the bubble is growing provides the momentum and velocity of the droplet in a substantially straight line direction towards a recording medium, such as paper.
Prior art thermal ink jet printers may operate in various process modes ranging from monochrome (black or white) to color highlighting; e.g. black and red; to full process color. For example, in U.S. Pat. No. 4,571,599, a multi-color thermal ink jet printer is disclosed, which utilizes four printheads with associated ink cartridges arranged linearly on a carriage which is moved past a recording medium. Each cartridge is filled with an ink appropriate for the color process mode selected. For a monochrome printing operation, each cartridge is filled with a black ink. For a color highlight mode, two cartridges may be filled with blank ink while two cartridges filled with, for example, magenta ink. For full process color, one carridge is filled with black ink while the other three are normally filled with cyan, magenta and yellow colored inks.
A severe disadvantage with prior art color printers is their lack of versatility if a change is desired in the color process mode. For example, if the system is operating in a full color process, and a switch to monochrome operation is desired, the chosen alternatives are to operate the system at the relatively slow color process speed, enabling only the cartridge having the blank ink, or replacing the three color cartridges with cartridges having blank ink. If the cartridge replacement mechanism is selected, the carriage can then be moved four times faster than in the process color mode. Generally, a change from a monochrome system (four black cartridges) to a process color system requires the replacement of three black cartridges by three color cartridges.
It would be desirable to provide a printing system which would be versatile enough to allow a rapid change in the ink delivery of the cartridges, thereby enabling changes between monochrome, color highlight and color process modes and without requiring cartridge replacement. The presnet invention is therefore directed towards a color printing system in which the inks contained in the cartridges are under operator control. The operator may select the particular combination of colors required for the process mode and initiate each reconfiguration operation while purging selected cartridges of the original ink supply and causing the selected cartridges to be refilled with an ink of the desired color. More particularly, the invention is directed towards a thermal ink jet printer including a reciprocating carriage adapted to convey a plurality of ink supply cartridges with integrally mounted thermal printheads forming a part thereof, means for stepping a recording medium a predetermined distance after each traversal of the carriage across the width of the recording medium, and means for propelling ink droplets from the nozzles of each printhead on demand, the printer further including:
a plurality of individual ink supply systems for supplying ink of a desired color to an associated ink cartridge, and
means for purging at least one of said supply systems of the ink supply contained therein and for refilling said system with an ink from at least one of said other ink supply systems.
The following prior art references appear to be relevant:
U.S. Pat. No. 4,554,556 to Hirata et al teaches an ink jet color plotter used for printing both alphanumeric characters and color plots at a high speed. A printhead assembly is reciprocally mounted on a carriage. Cyan, magenta and yellow inks are supplied to ink chambers of ink ejection heads 32, 34 and 36. Black ink is fed to all the ink chambers of the heads 38 and 40.
U.S. Pat. No. 4,596,990 to Hou discloses an ink jet printer which utilizes from two to n jets in a single printhead. The jets are aligned in a straight line substantially parallel to the relative printing direction. The use of multiple jet allows the printing speed to be increased two to n times faster depending upon the number of jets used.
U.S. Pat. No. 4,540,996 to Saito teaches a high speed multicolor ink jet printer. A recording head unit 15 is provided with a plurality of recording means offset from each other at predetermined intervals so that double recording and omissions may be prevented. The head unit 15 is reciprocally mounted on a carriage for movement across a recording sheet.